Neodymium trihydride, NdH3, with tysonite type structure

The crystal structure of trigonal neodymium trihydride has been refined by neutron powder diffraction on a two-phase deuteride sample (NdD3, space gro up P (3) over bar c1, a=6.6581(2) Angstrom, c=6.8778(2) Angstrom, T=293 K, LaF3 (tysonite) type structure). The hcp metal atom host structure contains three sorts of deuterium atoms, one occupying tetrahedral interstices with bond distances in the range Nd-D=2.36-2.58 Angstrom, and two having nearly triangular metal coordinations with bond distances of Nd-D=2.24 and 2.26 A . One of the triangular sites is ordered and the other disordered, in contr ast to previous work on rare-earth analogues that suggested both sites to b e disordered. NdD3 coexists with a cubic phase of composition NdD2.01 in wh ich deuterium atoms occupy tetrahedral and octahedral interstices of a ccp metal atom host structure (space group Fm (3) over barm, a=5.4324(2) Angstr om). (C) 2000 Elsevier Science B.V. All lights reserved.